Like all U interfaces, the UP0 interface is a two- wire interface for ISDN. It was intended by the ZVEI for company-specific interface solutions and replaces the UK0 interface standardized for the public sector. With the UP0 interface, directional separation takes place according to the ping-pong method.
Transmission via the UP0 interface takes place in half- duplex mode. The transmit data( TxD) and receive data( RxD) are transmitted separately in time in 125-microsecond frames. In order to guarantee both the two B channels with 64 kbit/s each, a D channel with 16 kbit/s as well as additional synchronization signals and guard periods, the duration of a binary signal is approx. 2 microseconds. This limits the range of the interface to approx. 2 to 4 km.